This invention relates to a process and apparatus for forming a window panel having an energy control film laminate and an acrylic or polycarbonate multi-panel window unit product having an energy control film laminate. In particular, the invention encompasses a method of applying a metallized transparent polymer film to the No. 2 surface of an insulating glass, acrylic or polycarbonate window unit.
The quest for reducing energy loss in homes and buildings has led to the development of an energy control film, applied to a surface of a window panel, to improve the shading coefficient and the R value thereby reducing total heat transmission and heat loss during the summer and winter months, respectively. Attempts at first were directed to designing solar energy control film sheets concerned with keeping sunlight's heat and glare from affecting the comfort of those inside a room (see, e.g., U.S. Pat. No. 2,744,021 and U.S. Pat. No. 3,290,203). These sheets, however, have been most widely used in geographical areas where the outside temperature rarely falls below 0.degree. C. Studies show, however, that windows not only contribute heavily to high air conditioning energy usage in the summer, but also contributes significantly to high heating costs in winter. The thermal conductance (or "U" value--the reciprocal of "R" value) of a single glazed window typically exceeds 5 kcal/.degree.C./hr/m.sup.2, whereas a well-insulated wall has a value less than 0.5 and a well-insulated ceiling has a U value less than 0.2. Consequently, heat can be lost through a conventionally glazed window at a rate over an order of magnitude greater than through insulated walls or ceilings.
Individuals having windows protected with solar control film frequently experience cold during winter for at least two reasons: solar-originating near infra-red energy is reflected back outside; and, heat inside the room is transferred to the window-pane by radiation and convection resulting in energy loss to the outside. Half of such loss is caused by radiation of internal infra-red energy from the skin of room occupants, as well as from objects in the room, to the solar control film whereby it is conducted to the outboard window panel and radiated to the outside. Attempts to maintain the advantages of solar energy control film while improving their poor insulating properties has led to the development of the energy control film disclosed in U.S. Pat. No. 4,226,910, assigned to Minnesota Mining and Manufacturing Company. This product, known as "Scotchtint" and related products, exclude externally originating heat and glare during the summer, but also substantially reduce heat loss from internally-originating infra-red radiation during the winter or, indeed, whenever the outside temperature is lower than the inside temperature.
It has been noted, however, in applying this film, or any other reflective metallized transparent polymer film, that dirt and dust particles become entrapped between the film and the window panel. Frequently, the film is inadvertently scratched or blemished during the application process. While some methods have been utilized in the prior art to reduce the entrapment of dust particles and to prevent scratches, these methods have not been generally acceptable. U.S. Pat. No. 3,837,952 discloses the application of a removable adhesive coated dust particle collecting member to remove dust particles from the glass panel. This prior art system also discloses a "wet method" which includes placing the glass panel on a table, hosing it down with water and applying an adhesive coated plastic sheet on the water layer, applying water to the exposed surface of the plastic sheet, and squeegeeing the exposed surface of the plastic sheet to press the plastic sheet into contact with the glass. Each glass and laminated sheet is then individually dried for approximately 24 hours to permit bonding of the laminate to the glass. This process, however, is time consuming and requires excessive materials, labor and drying space. In addition, due to the formation of static electricity during the manufacturing process, dust frequently becomes entrapped between the layers of the film and contacts the adhesive itself. This "wet method" merely picks up the dirt on the surface of the glass, it doesn't provided sufficient wetting of the film by passing it through a special bath to eliminate dust and dirt from the film's adhesive layer. No means are provided for eliminating static electricity to minimize the accummulation of dust and dirt particles on the film.
U.S. Pat. No. Re. 28,883 discloses a solar control film containing an integrally formed silcon release stratum on the surface of the film which serves as both a lubricant when the film is applied and as a protective coating to prevent scratches when the film is washed after being laminated in place. However, an energy control film which, otherwise, provides both winter and summer benefits will not function as desired if a release stratum is applied to the surface of the film. That is, the release stratum will eliminate the desired winter benefits since heat loss from internally originating infra-red radiation will be substantially increased. Consequently, the desired benefits of increasing the shading coefficient and the R value of a window unit to reduce total heat transmission and heat loss during the summer and winter months, respectively, will not be achieved with an integrally formed release stratum.
Furthermore, the prior art discussed above has been directed to the use of an energy control film on glass glazing units, rather than on acrylics or polycarbonates. Attempts in the prior art to apply metallized transparent polymer film to acrylic or polycarbonate surfaces have resulted in commercially unacceptable laminates. Surprisingly, it has been found that acrylics and polycarbonates give off water vapor and uncured monomers over a period of time; these gases create bubbles in the surface of the film and adversely affect its visual appearance and energy advantages.
The use of acrylics or polycarbonates would provide additional shatterproofing of the window panel, while permitting desirable thermal conductance not obtained by standard glass glazing units. Applying energy control film to the surface of such a panel would permit additional benefits making the structure commercially attractive. Additional benefits would be obtained by the use of an acrylic or polycarbonate window panels in an insulated window unit. This, however, has not been attempted in the prior art since the water vapor and uncured monomer problem noted above creates moisture buildup in the space between the acrylic or polycarbonate panels.